The present invention relates to an image-forming element for a printing apparatus including a support structure with a plurality of electrodes of a first type thereon and an electronic control unit for energizing electrodes.
An image-forming element of this type is usable as a so-called direct induction printer and is known from EP 0 803 783. In a direct induction printer, the image-forming electrodes on the surface of a drum body are covered by a dielectric layer, and a rotatable sleeve is disposed along the drum body such that the surfaces of the drum body and the sleeve form a gap which extends at right angles to the image-forming electrodes of the drum. A stationary magnetic knife is disposed inside of the sleeve for generating a magnetic field in the gap. A uniform layer of electrically conductive and magnetically attractable toner powder is applied to the surface of the sleeve. In an image-forming zone defined by the magnetic field in the gap, the toner powder is transferred onto the surface of the drum, depending on the voltage applied to the image-forming electrodes. Thus, by rotating the drum body and energizing the electrodes in accordance with image formation supplied to the control unit, a toner image is formed on the surface of the drum. Alternatively, a uniform layer of toner powder may be applied to the surface of the drum, and the toner powder may selectively be removed from the drum in accordance with the energizing pattern of the image-forming electrodes.
With the image-forming element of the prior art, the electronic control unit is provided with a number of electronic drivers for applying a voltage to each of the image-forming electrodes. Since each electrode is driven individually, one distinct driver is required for each image-forming electrode. For example, in the case of a printer with a resolution of 23.6 pixel per mm (600 dpi) and an image-forming element having a printing width of 300 mm, the number of drivers required for driving the image-forming electrodes is 7080. With the conventional image-forming elements, the manufacturing costs scale linearly with increasing print resolution or printing width. Moreover, when the number of drivers increases, the complexity of the manufacturing increases, due to the large number of interconnections required on a control unit.